A vascular aneurysm is the result of abnormal dilation of a blood vessel resulting from disease or a genetic condition that causes the arterial wall to weaken and expand. While aneurysms can potentially occur in any blood vessel, aneurysms occur predominantly in the aorta and peripheral arteries.
In the past, aortic aneurysms were commonly treated using open surgical procedures that, while effective, were often significantly life-threatening. Therefore, less invasive techniques were developed. One of these techniques involved the use of a catheter based delivery system that delivers an aortic graft to a target site at which the graft is to be deployed within the aorta.
In a catheter based delivery system, a less invasive entry point is used to introduce the aortic graft. The aortic graft is then advanced through the blood vessel to the site where the prosthesis is to be deployed (i.e. the aorta). An exemplary delivery system includes a delivery catheter with an inner tube (positioner) and an outer tube (sheath). The sheath is capable of axial movement. The aortic graft is attached to a flexible rod (cannula) and compressed within the sheath in front of the positioner. The delivery catheter is then maneuvered until the proximal end of the catheter containing the aortic graft is positioned in the vicinity of the target site. There, the positioner is held stationary while the sheath is withdrawn. The positioner serves to prevent the aortic graft from moving backwards as the sheath is withdrawn.
The types of stents that may be used with the aortic graft can be either self-expanding or balloon-expandable. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, trigger wires, or releasing diameter reducing ties. Use of trigger wires has been prevalent in maintaining the position of the aortic graft on the cannula until release.
Past systems have made use of trigger wires to secure the aortic graft at both its proximal and distal end. However, the use of suture loops to maintain the position of the aortic graft on the proximal end of the device has become favored because the threading of trigger wires through the vertices of a stent can often compromise the integrity of the aortic graft. The trigger wire can often become crimped when the stent is compressed within the sheath of the delivery device. If the trigger wires are crimped between the strut segments, the trigger wires and/or stent segments may become damaged during delivery, particularly for nickel-titanium stents that may be sensitive to surface imperfections. Furthermore, when compressing a cannula-cut stent having relatively acute bends to a significantly reduced radial profile, barbs disposed near the apices of the stent may become entangled with the stent struts and/or the trigger wires.
However, the deployment of an aortic graft that is attached to the delivery device by suture loops at the proximal end and trigger wires at the distal end requires a multitude of distinct and careful steps. For example, once the aortic graft is positioned in the vicinity of the target site, the sheath is first withdrawn to expose the proximal end of the cannula and the attached stent. The physician then rotates the cannula to release the top stent from the cannula. The cannula is withdrawn from between the aortic graft and the sheath is then further withdrawn to expose the entirety of the aortic graft. Finally, the trigger wire is withdrawn to release the distal end of the aortic graft and fully deploy the device.
However, because of the various steps necessary to release the aortic graft into the body as well as the high amount of precision needed to accomplish these tasks, physicians prefer to use devices that allow deployment of the prosthesis in the fewest number of steps.